Calibration of Voltmeter, Ammeter & Wattmeter using Potentiometer

Calibration is the process of verifying the accuracy of a result by comparing it with a standard value. In essence, it assesses the correctness of an instrument by contrasting it against a reference standard. This process enables us to identify errors in readings and make adjustments to voltages to achieve an ideal reading.

Calibration of Voltmeter
The circuit for the calibration of the voltmeter is shown in the figure below.

The circuit necessitates two rheostats: one serves to control the voltage, while the other is for fine - tuning. A voltage ratio box is employed to step - down the voltage to an appropriate level. The accurate value of the voltmeter is ascertained by measuring the voltage within the potentiometer's maximum possible range.

The potentiometer is capable of measuring the maximum achievable voltage values. If the readings of the potentiometer and the voltmeter do not match, negative or positive errors will manifest in the voltmeter's readings.

Calibration of Ammeter

The circuit for calibrating the ammeter is illustrated in the figure below.

A standard resistance is connected in series with the ammeter that is to be calibrated. A potentiometer is utilized to measure the voltage across the standard resistor. The current flowing through the standard resistance is determined by the formula described below.

where:Vs is the voltage across the standard resistor, as measured by the potentiometer.S is the resistance value of the standard resistor.This approach to ammeter calibration is highly accurate. The reason lies in the fact that both the value of the standard resistance and the voltage measured by the potentiometer can be precisely determined by the measuring instruments.Calibration of WattmeterThe circuit employed for calibrating the wattmeter is depicted in the figure below.

A standard resistance is connected in series with the wattmeter that requires calibration. A low - voltage power source supplies current to the current coil of the wattmeter. A rheostat is connected in series with the coil to regulate the current value.

The potential circuit is powered by the electrical supply. A volt - ratio box is utilized to reduce the voltage to a level that can be conveniently measured by the potentiometer. The actual values of voltage and current are measured using a double - pole double - throw switch. Subsequently, the accurate product of voltage and current (VI) is compared with the reading of the wattmeter.